This invention relates to aluminate phosphors emitting in the ultraviolet region of the electromagnetic spectrum, and more particularly relates to such phosphors containing Sr and/or Ca in combination with Ce, and also relates to lamps utilizing such phosphors.
Cerium activated aluminate phosphors are, in general, well known to the art. In particular, there has been considerable activity with phosphors based on the hexagonal aluminate compounds which consist of interleaved layers of spinel-like aluminum oxide and Me--O layers, where Me=Ca, Sr, Ba, La, Ce, K, Na and Cs. In addition, it is possible to replace some of the Al ions with Mg, Li, Zn, Ga and Sc. Historically, the alkali compounds have been called ".beta.-Al.sub.2 O.sub.3 " compounds, while the alkaline earth and rare earth compounds have been called "magnetoplumbite" compounds. Structural differences between these two classes are small. However, the alkali aluminates, where Me.dbd.Na, K, Cs, are not generally useful in conventional low pressure mercury vapor lamps due to a rapid deterioration of the phosphor in the lamp environment. British Pat. No. 1,452,083 to Philips Electronics and Associated Industries discloses many hexagonal aluminate phosphors with a variety of activators including Ce. Mg aluminate and alkaline earth (Ca or Sr) Mg aluminate phosphor compositions containing Ce ranging from about 0.03 mole percent (Example 1) are disclosed.
Isenberg, in U.S. Pat. No. 2,590,411, discloses alkaline earth aluminate phosphors activated by Ce. Wolfe, in U.S. Pat. No. 4,153,572, discloses YMg aluminates activated by Ce, and in U.S. Pat. No. 4,088,922, discloses Mg aluminates activated by Ce.
Aluminate phosphors coactivated by Ce and another element are also known. Coactivators include Mn and Dy (British Pat. No. 1,452,083) and Tb (British Pat. No. 4,026,816).
More recently Stevels, in J. Electrochem. Soc., Vol. 4, pp. 588-594, April '78, investigated luminescence of hexagonal aluminate phosphors containing Ca, Sr, Mg, Ba and La.